Showing papers in "Journal of Animal Ecology in 1995"

Stable isotopes in ecology and environmental science

Abstract: Contributors. Abbreviations. Introduction. 1. Stable isotope chemistry and measurement: a primer. Elizabeth W. Sulzman. Introduction. What isotopes are, what makes them distinct. Properties of ecologically useful stable isotopes. Technological advances and current trends in the ecological use of isotopes. Acknowledgments. References. 2. Sources of variation in the stable isotopic composition of plants. John D. Marshall, J. Renee Brooks, and Kate Lajtha. Introduction. Carbon isotopes. Nitrogen isotopes. Hydrogen and oxygen isotopes. Conclusions. References. 3. Natural 15N- and 13C-abundance as indicators of forest nitrogen status and soil carbon dynamics. Charles T. Garten, Jr, Paul J. Hanson, Donald E. Todd, Jr, Bonnie B. Lau, and Deanne J. Brice. Introduction. Significance of 15N-abundance to soil carbon sequestration. Vertical changes in soil 13C-abundance and soil carbon dynamics. Conclusions. Acknowledgments. References. 4. Soil nitrogen isotope composition. R. Dave Evans. Introduction. Sources of variation in soil 15N. Patterns of soil nitrogen isotope composition. Conclusions. References. 5. Isotopic study of the biology of modern and fossil vertebrates. Paul L. Koch. Introduction. Vertebrate tissues in the fossil record. Controls on the isotopic composition of vertebrate tissues. Preservation of biogenic isotope compositions by vertebrate fossils. Paleobiological applications. Conclusions. A post-script on workshops and literature resources. References. 6. Isotopic tracking of migrant wildlife. Keith A. Hobson. Introduction. Basic principles. Marine systems. Terrestrial systems (excluding deuterium). Using deuterium patterns in precipitation. Conclusions. References. 7. Natural abundance of 15N in marine planktonic ecosystems. Joseph P. Montoya. Introduction. Background. Isotopic variation in marine nitrogen. Source delineation and isotope budgets. Animal fractionation and food web processes. Isotopic transients in marine systems. Compound-specific nitrogen isotope analyses. Conclusions. Acknowledgment. References. 8. Stable isotope studies in marine chemoautotrophically based ecosystems: An update. Cindy Lee Van Dover. Introduction. Isotopic tracing of carbon at methane seeps. Whale falls. Hydrothermal vents. Conclusions. References. 9. Stable isotope ratios as tracers in marine food webs: An update. Robert H. Michener and Les Kaufman. Introduction. Methods of assessing food webs. Phytoplankton and particulate organic carbon. Phytoplankton and particulate organic nitrogen. Marine food webs. Stable isotopes in marine conservation biology. Conclusions. Acknowledgments. References. 10. Stable isotope tracing of temporal and spatial variability in organic matter sources to freshwater ecosystems. Jacques C. Finlay and Carol Kendall. Introduction. Overview of river food webs and stable isotope approaches. Stable isotope ratios of organic matter sources in stream ecosystems. C, N, and S isotopic variability and its applications in river ecology. Conclusions. Acknowledgments. References. 11. Stable isotope tracers in watershed hydrology. Kevin J. McGuire and Jeff McDonnell. Introduction. Basic concepts in watershed hydrology. Why are stable isotopes needed?. General concepts in isotope hydrology. Applications of isotope hydrology in watershed and ecosystem studies. Conclusions. Acknowledgments. References. 12. Tracing anthropogenic inputs of nitrogen to ecosystems. Carol Kendall, Emily M. Elliott, and Scott D. Wankel. Introduction. Isotopic compositions of major N sources to ecosystems. Processes affecting the isotopic composition of DIN. Separating mixing of sources from the effects of cycling. Applications to different environmental settings. What sources of agricultural and urban sources of nitrate can be distinguished using isotopes?. Other tools for tracing anthropogenic contaminants. Conclusions. References. 13. Modeling the dynamics of stable-isotope ratios for ecosystem biogeochemistry. William S. Currie. Introduction. Designing consistent model-data linkages and comparisons. Principles and techniques of stable isotope modeling. Conclusions. Acknowledgments. References. 14. Compound-specific stable isotope analysis in ecology and paleoecology. Richard P. Evershed, Ian D. Bull, Lorna T. Corr, Zoe M. Crossman, Bart E. van Dongen, Claire Evans, Susan Jim, Hazel Mottram, Anna J. Mukherjee, and Richard D. Pancost. Introduction. Why use compound-specific stable isotopes?. Analytical considerations in compound-specific stable isotope analysis. Applications of compound-specific stable isotope approaches in ecology and paleoecology. Conclusions. References. Index

The Coevolutionary Process

Abstract: In this text, Thompson advances a new conceptual approach to the evolution of species interactions - the geographic mosaic theory of coevolution. Thompson demonstrates how an integrated study of life histories, genetics and the geographic structure of populations yields a broader understanding of coevolution, or the development of reciprocal adaptations and specializations in interdependent species. Using examples of species interaction from a range of taxa, Thompson examines how and when extreme specialization evolves in interdependent species and how geographic differences in specialization, adaptation and the outcomes of interactions shape coevolution. Through the geographic mosaic theory, Thompson creates connections between the study of specialization and coevolution in local communities and the study of broader patterns seen in comparisons of the phylogenies of interacting species.

The Chironomidae: the biology and ecology of non-biting midges.

Abstract: Introduction. Taxonmomy, morphology and biogeography. Morphology. Systematics. Biogeography. Biology, behaviour and ecology. Biology of the eggs and first-instar larvae. The habitats of chironomid larvae. Larval food and feeding behaviour. The pupa and events leading to eclosion. Behaviour and ecology of adults. Life cycles and population dynamics. Production ecology. Species interactions and community structure. Interactions with humans. Nuisance, economic impact and possiblities for control. Medical significance. Classification of water-bodies and pollution. Chironomids as indicators of past environmental change. Chironomidae as food. Conclusions. References. Index.

Prey selection by tiger, leopard and dhole in tropical forests

Abstract: 1. Ecological factors influencing prey selection by tiger Panthera tigris, leopard Panthera pardus and dhole Cuon alpinus were investigated in an intact assemblage of large mammals in the tropical forests of Nagarahole, southern India, between 1986 and 1990. 2. Densities of large herbivores were estimated using line transects, and population structures from area counts. Carnivore diets were determined from analyses of scats (faeces) and kills. Selectivity for prey species was inferred from likelihood ratio tests comparing observed counts of scats to hypothesized scat frequencies generated from prey density estimates using parametric bootstrap simulations. Predator selectivity for size, age, sex and physical condition of prey was estimated using selection indices. 3. Ungulate and primate prey attained a density of 91 animals km -2 and comprised 89-98% of the biomass killed. Predators showed significant (P < 0.05) selectivity among prey species. Gaur Bos gaurus were preferred by tigers, whereas wild pig Sus scrofa were under-represented in leopard diet, and langur Presbytis entellus under-represented in dhole diet. 4. Tigers selected prey weighing more than 176 kg, whereas leopard and dhole focused on prey in the 30-175 kg size class. The average weights of principal prey killed by tiger, leopard and dhole were, respectively, 91.5 kg, 37.6 kg and 43.4 kg. Tiger predation was biased towards adult males in chital, sambar and wild pig, and towards young gaur. Dholes selectively preyed on adult male chital, whereas leopards did not. 5. These findings suggest that if there is choice, large carnivores selectively kill larger prey, and non-selective predation patterns reported from other tropical forests may be the result of scarcity of large prey. Because availability of prey in the appropriate size classes is not a limiting resource, selective predation may facilitate large carnivore coexistence in Nagarahole. Community structures of large carnivores in tropical forests may be highly sensitive to natural or human-induced variations in the relative densities of different size classes of prey.

Ecological morphology : integrative organismal biology

Abstract: Ecological morphology examines the relation between an animal's anatomy and physiology - its form and function - and how the animal has evolved in, and can inhabit, a particular environment. This book provides a synthesis of major concepts and a demonstration of the ways in which this integrative approach can yield rich and surprising results. Through this interdisciplinary study, scientists have been able to understand, for instance, how bat-wing design affects habitat use and bat diet; how the size of a predator affects its ability to capture and eat certain prey; and how certain mosquitoes have evolved physiologically and morphologically to tolerate salt-water habitats. "Ecological Morphology" also covers the history of the field, the role of the comparative method in studying adaptation and the use of data from modern organisms for understanding the ecology of fossil communities. This book provides an overview of the achievements and potential of ecological morphology for all biologists and students interested in the way animal design, ecology and evolution interact.

Selection for the timing of great tit breeding in relation to caterpillar growth and temperature

Abstract: 1. We investigated the relation between the timing of great tit breeding, measured as the mean date of laying the first egg in each clutch, the timing of caterpillar availability, measured as median pupation dates of winter moth, selection for laying dates, measured from the recruitment into the local breeding population in subsequent years, and temperature in the period after egg laying. 2. There was a significant positive correlation between the timing of the great tit's laying and the timing of the caterpillars. 3. In most years there was selection for earlier laying in this great tit population. The selection differentials were usually the same for male and female recruits. 4. The selection differential for laying date was strongly correlated (r = 0.84, n = 21, P <0.0001) with the difference in timing between birds and caterpillars. This difference in timing was in turn strongly correlated with temperatures in the period after egg laying. 5. When the period after the laying date was subdivided, the selection differential was strongly correlated with the mean temperature during the period when most birds were incubating. 6. We discuss six alternative hypotheses explaining a consistent selection differential for earlier laying. One of these is new and is based on the fact that the birds can delay their breeding more succesfully than they can speed it up, once they have started laying. [KEYWORDS: Caterpillar pupation; insectivorous birds;natural selection; timing of breeding; wytham wood Parus-major; clutch size; incubation; heritability;reproduction]

Sources, sinks and pseudo-sinks

Abstract: It has been suggested that the habitats which a species occupies can be divided into sources and sinks, depending on whether or not local reproduction is sufficient to balance mortality. Source populations are those where reproduction exceeds mortality, surplus individuals dispersing to sink populations where mortality exceeds local reproduction. Sink populations would not be viable in the absence of immigration. A difference equation model is constructed to show that sources and sinks cannot be identified from a simple comparison of the demographic rates between populations, as measured by the numbers of births and deaths. Viable populations may appear to be non-viable simply because the dispersal of individuals into them depresses fecundity or increases mortality as a result of density-dependence. The consequence is that local recruitment appears insufficient to balance local mortality. Viable populations that appear as sinks, as a result of the dispersal of individuals into them, are termed here as 'pseudo-sinks'. They will clearly be difficult to distinguish from genuine sinks on the basis of a simple comparison of the numbers of births and deaths in different populations. Examples of source and genuine sink populations and the data required to establish them are discussed.

Spatial analysis by distance indices

Abstract: 1. A new method of quantifying spatial pattern was introduced for two-dimensional mapped data, with an associated index of aggregation and a test for departures from randomness, based on an attractive algorithm in which individuals in the sample move to a regular arrangement which resembles a hexagonal lattice, using Voronoi tessellations. The algorithm incorporates a biological model for the dispersal of individuals from a source, in which each individual is assigned a dynamic territory. The method is one of a class known as Spatial Analysis by Distance IndicEs (SADIE). 2. Two diagnostic plots were introduced, each based on the distance of the sample from the final, regular arrangement, to aid the description of the observed spatial pattern. 3. By backtracking from the observed sample points away from the final arrangement, the presence of clusters in the sample may be detected more easily, and heuristic estimates derived of the cluster foci. 4. Examples are given for seven sets of data, with analyses of over 20 subsets at several spatial scales, concerning: aphids, beetle larvae, ant mounds, sparrowhawk nesting territories, pine seedlings, redwood seedlings, and biological cells.

Individual differences in resource use, growth and emigration under the influence of a dominance hierarchy in fluvial red-spotted masu salmon in a natural habitat

Abstract: The relationships between dominance status and individual differences in foraging behaviour, habitat use, growth and emigration were examined for fluvial red-spotted masu salmon, Oncorhynchus masou ishikawai, in a mountain stream. Size-structured linear dominance hierarchies were recognized among individuals inhabiting the same stream pools. Observations on space utilization and foraging behaviour revealed fish to be either territorial or nonterritorial. Within each local pool, dominant fish exclusively occupied the mid or surface layer of the pools as foraging territories, whereas subordinates adopted nonterritorial tactics, primarily utilizing the bottom layer. Of the territorial fish, more dominant individuals tended to occupy focal points nearer the pool inlet, where they had priority of access to drifting food items. These fish showed higher actual foraging rates, feeding upon larger prey than their subordinates. This foraging advantage resulted in their having larger daily growth increments. The more dominant fish in each pool exhibited a more sedentary tendency than their subordinates. Population densities in the pools did not fluctuate appreciably owing to both emigration of nonterritorial subordinates and immigration. These results support the hypothesis that unequal resource partitioning among individuals subject to a dominance hierarchy plays an important role in their density-dependent population regulation.

Models in Biology: Mathematics, Statistics and Computing

Abstract: MODELS FOR SINGLE POPULATIONS AND PROCESSES Deterministic Models of Growth and Decline Deterministic Genetic Models Stochastic Models of Genetic, Environmental and Sampling Variation Structured Stochastic Models: Models with Both Deterministic and Stochastic Elements Fitting Models: Constants, Straight Lines, Polynomials and Non-Linear Models BIOLOGICAL COMPARISONS AND DESIGN ISSUES Statistical Methods for Comparing Biological Populations and Processes Sampling, Controlling and Measuring the Random and Systematic Variation: Design of Experiments and Surveys BIOLOGICAL INTERACTIONS The Mathematics of Interaction Biochemistry and Physiology Ecology and Epidemiology Advanced Model Fitting ADVANCED TOPICS Transport and Diffusion Statistical Analysis of Pattern and Sequence: Temporal and Spatial Series and DNA Sequences Descriptive Models of Complex Relationships: Multiple Regression and Response Surface Models Models of the Brain: Neural Networks GLOSSARY, TABLES, REFERENCES AND INDEX Mathematical Glossary Statistical Tables References Index.

Interspecific aggression and habitat selection by Amazonian birds

Abstract: We report that interspecific territoriality is a common spacing mechanism among closely related bird species distributed along a primary successional gradient in the meander belt of an Amazonian whitewater river. In the first phase of the research, we mapped the territories of more than 330 bird species in large census plots encompassing the complete successional gradient. We found species pairs in over 20 genera that showed contiguous but non-overlapping territories, such that early stages of the successional gradient were occupied by one member of the pair, and later stages by the other. Other species pairs showed additional types of spatial relationships, including partially overlapping and completely overlapping territories. Using reciprocal heterospecific playback experiments, we tested for the existence of aggressive interactions between the members of species pairs (usually congeners) showing all three types of spatial relationship. Among 12 species pairs showing contiguous, non-overlapping territories, 10 showed evidence of interspecific aggression (approach to the playback speaker). In eight of these 10 cases, the responses were markedly asymmetric. Target individuals of one species approached the speaker, whereas individuals of the other species remained in place or moved away. The heavier species was consistently the aggressor. In six species pairs showing partial territorial overlap along the successional gradient, only one species displayed statistically significant interspecific aggressiveness, although some individuals in all six pairs approached or avoided the speaker. In species pairs distributed with completely overlapping territories, we found interspecific aggression in only one of five genera tested. We suggest that spatial segregation of congeneric bird species on habitat gradients (presumably including elevational gradients), is commonly underpinned by interspecific territoriality mediated through directed, asymmetrical interspecific aggression. Aggressive asymmetry suggests a despotic model of habitat occupancy, in which the larger species occupies the more productive end of habitat gradients, and the smaller species occupies less productive habitats. The pronounced successional gradients characteristic of Amazonia may explain much of the increased species richness, especially within genera, of Amazonian bird communities.

Quantitative genetic studies of behavioral evolution

Abstract: This text examines the theory and methods of quantitative genetics and presents case studies that illustrate the many ways in which the methods can be applied. The author brings together current theoretical and empirical studies to show how quantitative genetics can illuminate topics as diverse as sexual selection, migration, sociality and aggressive behaviour. Nearly half of the chapters focus on conceptual issues, ranging from quantitative genetic models to the complementary roles of quantitative genetic and optimality approaches in evolutionary studies. Other chapters illustrate how to use the techniques by providing surveys of research fields, such as the evolution of mating behaviour, sexual selection, migration and size-dependent behavioural variation. The balance of the volume offers case studies of territoriality in fruit flies, cannibalism in flour beetles, mate-attractive traits in crickets, locomotor behaviour and physiology in the garter snake, and cold adaptation in the house mouse. Taken together, these studies document both the benefits and pitfalls of quantitative genetics. This book aims to show the advanced student and scholar of behavioural evolution and genetics the many powerful uses of quantitative genetics in behavioural research.

Habitat fragmentation and the individual : tawny owls Strix aluco in woodland patches

Abstract: The aim of this study was to examine tawny owls Strix aluco in continuous and fragmented woodland habitats to determine the effect of fragmentation on behaviour, breeding success and turnover. Information on home range and territorial behaviour was obtained from 23 radiotagged individuals. Eight of these were in one large wood (continuous) and the rest in an area containing 4 ha and in up to 45% of wood buildings > grassland > arable areas. Owls utilized the grassland and arable areas by hunting from the ground. In continuous woodland owl home ranges overlapped more and they were more often involved in territorial behaviour than those in fragmented woodland. There was a negative relationship between small mammal abundance and wood size. For all years combined there was a quadratic relationship between wood size and breeding success, suggesting that owls perform better in intermediate-sized woods. Turnover was highest in the smallest woods and lowest in the intermediate woods. It is concluded that the intermediate woods, where food is abundant and energetic costs are not great, present an optimum habitat for tawny owls in this area. The study indicates that data on breeding success and turnover are essential in determining the effects of habitat fragmentation and that these effects may not be easy to predict, given information from non-fragmented areas.

Population Demography of Antarctic Fur Seals: The Costs of Reproduction and Implications for Life-Histories

Abstract: 1. This study examined the costs of reproduction in terms of future survival and reproduction in female Antarctic fur seals from Bird Island, South Georgia. It used mark-recapture data from 11 consecutive years, including 3 years when several indices showed that food availability was well below average. 2. Population age structures were used, in conjunction with the measured age-specific survival rates, to estimate the rate of increase of the population as 10.7% per annum. 3. The average annual survival rate was 0.83 (SD = 0.10) with a range from 0.65 to 0.93. Survival rate showed no trend through time but was weakly correlated with pup growth rate, suggesting that it may be influenced by availability of food. Survival rate was unrelated to any other environmental or demographic parameter including population size. 4. There was no evidence of senescence. Survival rate was not related to year of birth or age, after accounting for variation due to pregnancy and calendar year. Survival was reduced as a result of pregnancy which accounted for 40-50% of adult female mortality. This effect was greatest in the age classes with the highest reproductive output (ages 5-8 years). 5. Mean pregnancy rate was 0.70 (SD = 0.11) with an interannual range of 0.59-0.88. Although females normally produced their first pups at age 3-4 years, pregnancy rate peaked at age 8 years and declined thereafter. Otherwise pregnancy rate was unrelated to the environmental or demographic variables we tested. Food availability during the pup-rearing period had no effect on pregnancy rate. 40-50% of failures to become pregnant related to animals having been pregnant in the previous year. 6. Reproduction incurs costs to females, in terms of reduced survival and future fecundity, and consequently, on average, females which survive longest tend to do so because they have lower fecundity.

Synchrony in Tetraonid Population Dynamics

Abstract: We studied temporal and spatial synchrony of population fluctuations in the capercaillie (Tetrao urogallus), the black grouse (Tetrao tetrix) and the hazel grouse (Bonasa bonasia) in Finland. The data consist of route censuses (20 000-30 000 km annually) performed in 11 provinces during 1964-83. The population data for the three species in each province were standardized to zero mean and unit variance. Cross-correlation analysis indicates that population dynamics of the three species in every area are in rather good temporal synchrony. Moreover, with the aid of k-means clustering, the 11 provinces could be merged into four regions, indicating large-scale synchrony in dynamics of the three tetraonid species. Because it is obvious that this synchrony cannot be due only to the similar life histories of these species, we explored whether it could be influenced by a common synchronizing factor affecting all the species simultaneously. In order to do this we used a Leslie matrix-based simulation approach. In this model there is a stochastic hit of breeding failure at a given average interval. This failure was shown to synchronize the population dynamics of the species with primarily different life tables.

Body Size, Population Density, and the Energetic Equivalence Rule

Abstract: 1. We critically evaluated the Energetic Equivalence Rule (EER) with regard to its underlying theoretical framework, its dependence of a particular relationship between population density and body size, and the way it is calculated. 2. We found it to be theoretically incorrect, not supported by empirical data on maximum population density and body size relationships, and that its calculation is misleading. In particular, we found a general pattern underlying the allometry of maximum population density, which stresses the correspondence between the documented linear patterns and triangular relationships between both variables. 3. Two independent data sets, one for mammals and another for intertidal invertebrates, showed that medium-size species attain higher population densities, and that population density decreases towards larger and smaller sizes. 4. A more direct calculation of population energy use for mammalian primary consumers, based on measured metabolic rates, showed that populations'energy use fluctuates widely among species and that its upper limit is not independent of body size but peaks at a body size of about 100 g, and decreases toward both smaller and larger body sizes. 5. Diet also has a strong effect on this relationship. Omnivores show a positive relationship between population energy use and body size, while this is negative for carnivores and insectivores

Life-history strategy of the herring gull : changes in survival and fecundity in a population subjected to various feeding conditions

Abstract: The present study compares breeding parameters and adult survival rate in a herring gull colony before and after the closing of a large refuse tip where breeders used to find most of their food. During the first study period (1983-88) food of human origin was abundant and virtually always available. During the second period (1989-90) such food was scarce. The annual adult survival rate was time-dependent. It varied from 0.826 (SE = 0.031) in 1987-88 to 0.975 (SE = 0.022) in 1985-86. The average survival rate calculated for 1983-90 was 0.881 (SE = 0.014). There was no significant difference in adult survival between males and females. The closure of the refuse tip was not followed by a significant decrease in adult survival rate. After the refuse tip was closed, mean clutch size and mean production of young per breeding pair decreased by 6.7% and 49.1%, respectively. Mean adult body weight decreased by 4.6% for males and by 4.7% for females. The proportion of non-breeders among former breeders and the proportion of 3- and 4-year-old individuals among ringed birds did not change after closure of the tip. The results are discussed in terms of the life-history theory, which predicts that in long-lived species a decrease in food supply should affect fecundity before affecting adult survival.

Differential response by males and females to brood manipulations in the Pied Flycatcher : Energy expenditure and nestling diet

Abstract: A brood manipulation experiment on pied flycatchers Ficedula hypoleuca breeding in central Spain was performed in order to study the response of males and females to different levels of brood demand. Modal broods of six young were manipulated on the day after hatching to give brood sizes of eight (enlarged), six (control) and four (reduced). Energy expenditure of parent birds feeding nestlings of 6 and 12 days of age was measured using the doubly labelled water technique. There was no effect of chick age on daily energy expenditure (DEE) of males and females. Brood size had a significant positive effect on the daily energy expenditure of males and their number of feeding visits to the nest. However, there was no relationship between brood size and the energy expenditure or visiting rate of females. Camera nestboxes were used to record the prey brought to the manipulated broods. There was no effect of brood size on the mean number of prey brought per feeding visit. The prey brought by males and females were similar, and there was no apparent effect of brood size on diet. Nestling mortality, tarsus length and body weight of nestlings were not affected by brood size. This suggests that the increased feeding response and energetic expenditure by males compensates for the increased food demand in the enlarged broods. Performing brood manipulations and extrapolating feeding activity to energetic costs of reproduction needs to be approached with caution, as evidenced by the lack of relationship between female nest visits and DEE. Preferably the energetic exertion of both parents should be measured directly.

Parasites and food web patterns

Abstract: 1. We expanded two previously studied food webs, those of the Ythan estuary and Loch Leven, by the documentation of metazoan endoparasites present in each system. The resulting webs are the first in the literature to contain substantial numbers of parasites. 2. Four versions of each web were produced, containing increasing numbers of parasite species and parasite-host links. Each version was analysed for four food-web patterns: food-chain length, linkage'density, proportions of top, intermediate and basal species and omnivory. 3. The patterns were not generally consistent with those previously reported in the literature. In particular, increasing the numbers of parasitic links increased the proportions of top species, and the percentage of omnivory, in both the well (Ythan) and poorly (Loch Leven) documented webs. 4. These results were dependent on the choice of biological or «tropho» species. Splitting the parasites documented in the Ythan web into separate life-history stages produced a greater conformity of omnivory and linkage density with previous webs, but a larger deviation of the proportion of top species from previously recorded values. 5. The cascade model accurately predicts the length of food chains in the Ythan web. This suggests that the feeding hierarchy assumed in the model may exist in nature, but that body size alone is not sufficient to explain it

Holling's functional response model as a tool to link the food-finding mechanism of a probing shorebird with its spatial distribution

Abstract: 1. Knots Calidris canutus are high-arctic breeding shorebirds which spend the nonbreeding season in intertidal areas where they feed on small buried molluscs which are swallowed whole. We tested whether their intake rate can be adequately described by a functional response model (the disc equation of Holling) assuming prey detection by direct touch. 2. Knots were fed two bivalve species (Macoma balthica and Cerastoderma edule) of different size and at different density and in Macoma at variable depth on small areas of soft Sediment. Five different individuals were used in feeding trials during which six prey were allowed detection and ingestion. 3. Knots perfectly obeyed the two basic assumptions of Holling's disc equation: neither the instantaneous area of discovery nor the handling time changed with variation in prey density. 4. However, two predictions for prey perception by direct touch (that the instantaneous area of discovery is a positive function of shell size and a negative one of prey depth) were rejected. The instantaneous area of discovery was usually also higher than predicted from the area touched by probing knots. 5. Knots may, therefore, use a 'remote sense' to locate buried hard-shelled prey. Gerritsen, van Heezik & Swennen (1983) showed that knots do not use taste to discover bivalves at a distance. We argue that the detection involves a self-induced pressure mechanism rather than a passive sense for vibrations, since it is unlikely that static bivalve prey emit such signals just after experimental handling. 6. Whatever the exact prey detection mechanism, the recorded (high) value for the instantaneous area of discovery of deep-living bivalve prey is in accord with the observation that knots use large areas of intertidal flat in the western Dutch Wadden Sea where bivalve stocks are too low to support knots according to a previous functional response model invoking direct touch.

Dynamic host feeding by the parasitoid Aphytis melinus: the balance between current and future reproduction

Abstract: 1. In many species of parasitoid Hymenoptera, adult females can use hosts either for oviposition or «host feeding». Oviposition is current reproduction and host feeding represents investment towards future reproduction. 2. We investigated the influences of egg load, diet, age, experience and host size on host-feeding behaviour in the aphelinid parasitoid Aphytis melinus attacking oleander scale Aspidiotus nerii (Homoptera: Diaspididae). Hosts were either rejected, used exclusively for host feeding, used for both oviposition and host feeding concurrently, or used exclusively for oviposition. When hosts were used for both oviposition and host feeding, parasitoid progeny did not develop to adulthood. 3. Behavioural records were analysed with the logistic regression model, a statistical tool for assessing the relative contributions of multiple, potentially correlated, variables. 4. Variation in egg load was obtained by (i) using diet and age treatments to manipulate the rate of egg resorption by parasitoids and (ii) taking advantage of size-related differences in egg load. Parasitoids with lower egg loads were more likely to host feed than to ovipost. This result is consistent with recently developed theory. 5. During their first-ever encounter with a host, parasitoids that had been fed a pure sucrose diet during their adult life were more likely to host feed than were parasitoids fed a sucrose diet supplemented with yeast. 6. Contrary to theoretical predictions, younger parasitoids were not more likely to host feed than older parasitoids. 7. Smaller hosts were (i) more frequently used for host feeding than were larger hosts, and (ii) less suitable for progeny development than were larger hosts

Female/female competition in European badgers Meles meles: effects on breeding success

Abstract: We present data on the effects of female/female competition on the reproductive success of European badgers Meles meles in Britain. While a single, dominant female usually suppresses reproduction in other female group members, elsewhere up to four females may breed successfully in each group. Across Britain, the mean number of breeding females per social group decreases in populations living at high latitudes, where food availability and population density are relatively low. Within our study population in southern England, the number of breeding females in each social group increased with the quality of the group territory. In our study population, all females aged 3 years and older became pregnant, but a proportion of females lost their litters during gestation or around the time of birth. The proportion of females that lost their litters was higher in larger groups. However, mean litter size at weaning remained roughly constant despite variation in the number of females lactating, and preweaning cub mortality appeared to be low. Females tended to disperse away from very large groups, and may have increased their chances of breeding in this way. These results suggest that females competed for breeding status, but that there was little competition among females thereafter. The characteristics of females that produced cubs successfully differed between the 2 years when this study was carried out. Only females in relatively good condition bred successfully following a very dry summer, when food availability was low. However, when food availability was high, following a wet summer, females were in better condition on average and breeding success appeared to be related to social status. We suggest that this reflected a difference in the structure of competition between the two years. In contrast with the situation in other social carnivores, reproductive suppression in badgers appears to be a response to female/female competition for resources, rather than a need for co-operative care of the young. Although alloparental care occurred in at least one badger population, this population had the lowest, rather than the highest, level of reproductive suppression.

Progeny and sex allocation decisions of the polyembryonic wasp Copidosoma floridanum.

Abstract: 1. The reproductive biology of the polyembryonic encyrtid wasp Copidosoma floridanum was examined in a series of laboratory experiments and related to observations from field collections. Females laid one or two eggs per host, producing broods comprised of all males, all females, or both sexes (mixed). Each egg produced multiple embryos that developed into either precocious larvae that never became adult or reproductive larvae that developed into reproductive adults. 2. The age of the host-egg when it was parasitized was found to have a substantial effect on offspring clutch sizes and sex ratios. (i) The clutch sizes and overall survivorship of female and mixed broods decreased with increasing host-egg age, whereas male clutch sizes and survivorship were relatively unaffected by host-egg age. (ii) Offspring sex ratios (proportion males) of mixed broods were higher in older hosteggs. (iii) Body sizes of males and females were negatively correlated with clutch size. Larger females had higher fecundities and larger males had greater mating abilities. 3. Host-egg age also affected competitive asymmetries between males and females. In young host-eggs, female precocious larvae were much more abundant than males and were instrumental in reducing the number of males in mixed broods. In older host-eggs, the numbers of male and female precocious larvae were much lower, and were approximately equal. As a result, sex ratios of mixed broods in older host eggs were closer to equality. 4. Ovipositing females responded to host-egg age and host encounter rates when making oviposition decisions. Females laid more female eggs in younger hosts and more mixed broods in older hosts. Females laid more mixed broods when encounter rates were low and more female broods when encounter rates were high